Search for Production of Invisible Final States in Single-Photon Decays of \(Υ(1S)\)

Abstract

We search for single-photon decays of the (Υ(1S)) resonance, (Υ→γ+) invisible, where the invisible state is either a particle of definite mass, such as a light Higgs boson (A^0), or a pair of dark matter particles, (χ\overline{χ}). Both (A^0) and χ are assumed to have zero spin. We tag (Υ(1S)) decays with a dipion transition (Υ(2S)→π^{+}π^{−}Υ(1S)) and look for events with a single energetic photon and significant missing energy. We find no evidence for such processes in the mass range (m_{A^{0}}≤9.2 GeV) and (m_{χ}≤4.5 GeV) in the sample of (98×10^{6} Υ(2S)) decays collected with the BABAR detector and set stringent limits on new physics models that contain light dark matter states.